Radiation-curable polyurethane

Abstract

A radiation-curable polyurethane is obtained from the reaction of a low free diisocyanate polyurethane prepolymer and an acrylic monomer.

1. A radiation-curable polyurethane produced by the process which comprises:
 (a) reacting at least one diisocyanate monomer with a combination of a high molecular weight polyol and a low molecular weight polyol to provide a polyurethane prepolymer containing unreacted diisocyanate monomer, wherein each polyol is selected from the group consisting of polyether, polyester, polycarbonate, polycaprolactone and hydrocarbon polyols having a number average molecular weight of from about 60 to about 12,000;  
 b) removing unreacted diisocyanate monomer from the polyurethane prepolymer to provide polyurethane prepolymer of reduced unreacted diisocyanate monomer content; and,  
 c) reacting the polyurethane prepolymer of reduced unreacted diisocyanate monomer content with an acrylic monomer to provide radiation-curable polyurethane.  
 
     
     
       2. The radiation-curable polyurethane of  claim 1  wherein the diisocyanate monomer is at least one diisocyanate monomer selected from the group consisting of 2,4 and 2,6 toluene diisocyanate, 4,4′-diphenyl methane diisocyanate, p-phenylene diisocyanate, tolidene diisocyanate, hexamethylene diisocyanate, tetramethylxylene diisocyanate, isophorone diisocyanate and dicyclohexylmethane diisocyanate. 
     
     
       3. The radiation-curable polyurethane of  claim 1  wherein the polyether polyol is represented by the general formula HO(RO) n H, wherein R is an alkylene radical and n is an integer large enough that the polyether polyol has a number average molecular weight of at least about 250. 
     
     
       4. The radiation-curable polyurethane of  claim 3  wherein the polyether polyol is a polytetramethylene ether glycol. 
     
     
       5. The radiation-curable polyurethane of  claim 1  wherein the low molecular weight polyol is an aliphatic polyol selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, and the like. 
     
     
       6. The radiation-curable polyurethane of  claim 1  wherein the low molecular weight polyol is less than about 20% of the combination of high molecular weight polyol and low molecular weight polyol. 
     
     
       7. The radiation-curable polyurethane of  claim 6  wherein the low molecular weight polyol is up to about 15% of the combination of high molecular weight polyol and low molecular weight polyol. 
     
     
       8. A radiation-curable polyurethane produced by the process which comprises:
 (a) reacting at least one diisocyanate monomer with at least one polyol to provide a polyurethane prepolymer containing unreacted diisocyanate monomer, wherein the polyol is selected from the group consisting of polyether, polyester, polycarbonate, polycaprolactone and hydrocarbon polyols having a number average molecular weight of from about 100 to about 12,000, and wherein the polyester polyol is a mixture of a polyester of butanediol, hexanediol and adipic acid;  
 (b) removing unreacted diisocyanate monomer from the polyurethane prepolymer to provide polyurethane prepolymer of reduced unreacted diisocyanate monomer content; and,  
 (c) reacting the polyurethane prepolymer of reduced unreacted diisocyanate monomer content with an acrylic monomer to provide radiation-curable polyurethane.  
 
     
     
       9. The radiation-curable polyurethane of  claim 1  wherein the polyurethane prepolymer is of the general structure ABA wherein A denotes diisocyanate and B denotes a polyol. 
     
     
       10. The radiation-curable polyurethane of  claim 1  wherein the removal of unreacted diisocyanate monomer from the polyurethane prepolymer is accomplished through a process of distillation. 
     
     
       11. The radiation-curable polyurethane of  claim 10  wherein the process of distillation is accomplished through an agitated film distillation system. 
     
     
       12. The radiation-curable polyurethane of  claim 11  wherein the agitated film distillation system comprises continuous units with internal condensers that can be combined in series. 
     
     
       13. The radiation-curable polyurethane of  claim 10  wherein the process of distillation utilizes a wiped film vacuum distillation process. 
     
     
       14. The radiation-curable polyurethane of  claim 1  wherein the removal of unreacted diisocyanate monomer from the polyurethane prepolymer reduces the content of unreacted diisocyanate monomer polyurethane prepolymer to less than about 2% by weight. 
     
     
       15. The radiation-curable polyurethane of  claim 14  wherein the removal of unreacted diisocyanate monomer from the polyurethane prepolymer reduces the content of unreacted diisocyanate monomer polyurethane prepolymer to less than about 0.5% by weight. 
     
     
       16. A radiation-curable polyurethane produced by the process which comprises:
 (a) reacting at least one diisocyanate monomer with at least one polyol to provide a polyurethane prepolymer containing unreacted diisocyanate monomer;  
 (b) removing unreacted diisocyanate monomer from the polyurethane prepolymer to provide polyurethane prepolymer of reduced unreacted diisocyanate monomer content, wherein the removal of unreacted diisocyanate monomer from the polyurethane prepolymer reduces the content of unreacted diisocyanate monomer polyurethane prepolymer to less than about 0.1% by weight; and,  
 (c) reacting the polyurethane prepolymer of reduced unreacted diisocyanate monomer content with an acrylic monomer to provide radiation-curable polyurethane.  
 
     
     
       17. The radiation-curable polyurethane of  claim 1  wherein the acrylic monomer possesses at least one reactive functionality. 
     
     
       18. The radiation-curable polyurethane of  claim 17  wherein the acrylic monomer possessing at least one reactive functionality is selected from the group consisting of vinyl carboxylic acid, acrylic acid, methacrylic acid, aminoalkyl acrylates, aminoalkyl methacrylates, hydroxyalkyl acrylates, hydroxyalkyl methacrylates and mixtures thereof. 
     
     
       19. The radiation-curable polyurethane of  claim 18  wherein the hydroxyalkyl acrylate is selected from the group consisting of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutylacrylate and mixtures thereof. 
     
     
       20. The radiation-curable composition of  claim 1  wherein the polyurethane prepolymer of reduced unreacted diisocyanate monomer content is end-capped with an acrylate. 
     
     
       21. The radiation-curable polyurethane of  claim 1  wherein the reaction of at least one diisocyanate monomer with the combination of polyols provides for a molar excess of diisocyanate monomer over polyol. 
     
     
       22. The radiation-curable polyurethane of  claim 21  wherein the molar excess of diisocyanate monomer over polyol is from about 2:1 to about 30:1 molar ratio. 
     
     
       23. The radiation-curable polyurethane of  claim 22  wherein the molar excess of diisocyanate monomer over polyol is from about 3:1 to about 18:1 molar ratio. 
     
     
       24. The radiation-curable polyurethane of  claim 23  wherein the reaction of at least one diisocyanate monomer with the combination of polyols has a solvent added thereto. 
     
     
       25. A radiation-curable polyurethane produced by the process which comprises:
 (a) reacting at least one diisocyanate monomer with at least one polyol to provide a polyurethane prepolymer containing unreacted diisocyanate monomer, wherein the reaction of at least one diisocyanate monomer with at least one polyol provides for a molar excess of diisocyanate monomer over polyol from about 3:1 to about 20:1 molar ratio, and wherein the reaction of at least one diisocyanate monomer with at least one polyol has a solvent added thereto, wherein the solvent is selected from the group consisting of dimethyl adipate and dimethyl phthalate;  
 (b) removing unreacted diisocyanate monomer from the polyurethane prepolymer to provide polyurethane prepolymer of reduced unreacted diisocyanate monomer content; and,  
 (c) reacting the polyurethane prepolymer of reduced unreacted diisocyanate monomer content with an acrylic monomer to provide radiation-curable polyurethane.  
 
     
     
       26. The radiation-curable polyurethane of  claim 1  formed from a prepolymer of step (b) having a NCO content of at least about 70% of the theoretical NCO content. 
     
     
       27. The radiation-curable polyurethane of  claim 1  formed from a prepolymer of step (b) having a NCO content of at least about 80% of the theoretical NCO content. 
     
     
       28. The radiation-curable polyurethane of  claim 18  wherein the hydroxyalkyl acrylate has a ratio of available hydroxyl functionality to the available NCO content of the polyurethane prepolymer of reduced unreacted diisocyanate monomer content of from about 0.9:1 to about 1.2:1. 
     
     
       29. The radiation-curable polyurethane of  claim 28  wherein the hydroxyalkyl acrylate has a ratio of available hydroxyl functionality to the available NCO content of the polyurethane prepolymer of reduced unreacted diisocyanate monomer content of from about 1.05:1 to about 1.10:1. 
     
     
       30. The radiation-curable polyurethane of  claim 1  wherein step (c) can have added thereto one or more inhibitors of free radical reactions in an amount of from about 50 ppm to about 1% by weight. 
     
     
       31. The radiation-curable polyurethane of  claim 30  wherein the inhibitor of free radical reactions is 4-methoxyphenol. 
     
     
       32. The radiation-curable polyurethane of  claim 1  wherein step (c) can have added thereto one or more catalysts in an amount of up to about 3% by weight. 
     
     
       33. The radiation-curable polyurethane of  claim 1  wherein at the temperature of about 50° C. the viscosity is from about 500 to about 28,000 cps. 
     
     
       34. A radiation-curable polyurethane comprising:
 a) a polyurethane prepolymer terminated with a diisocyanate monomer selected from the group consisting of 2,4- and 2,6-toluene diisocyanate, 4,4′-diphenyl methane diisocyanate, p-phenylene diisocyanate, tolidene diisocyanate, hexamethylene diisocyanate, tetramethylxylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane diisocyanate, said polyurethane prepolymer being the reaction product of one or more of the said diisocyanate monomers and at least one polyol selected from the group consisting of polyether, polyester, polycarbonate, polycaprolactone and hydrocarbon polyols having a number average molecular weight of from about 250 to about 10,000 from which unreacted diisocyanate monomer has been removed; said polyurethane prepolymer comprising no more than about 2 wt % free diisocyanate monomer and having at least about 80% of theoretical NCO content for pure ABA structure and;  
 b) an acrylic monomer possessing at least one reactive functionality selected from the group consisting of vinyl carboxylic acids, acrylic acid, methacrylic acid, aminoalkyl acrylates, aminoalkyl methacrylates, hydroxyalkyl acrylates, hydroxyalkyl methacrylates and mixtures thereof, said radiation-curable polyurethane containing a ratio of available hydroxy functionality of the hydroxyalkyl acrylate to NCO content of the prepolymer of reduced unreacted diisocyanate monomer content of from about 0.9:1 to about 1.2:1.  
 
     
     
       35. A substrate coated with a radiation-curable polyurethane produced by the process of  claim 1 . 
     
     
       36. A substrate coated with a radiation-curable polyurethane produced by the process of  claim 8 . 
     
     
       37. A substrate coated with a radiation-curable polyurethane produced by the process of  claim 16 . 
     
     
       38. A substrate coated with a radiation-curable polyurethane produced by the process of  claim 25 . 
     
     
       39. The radiation-curable polyurethane of  claim 1  wherein the high molecular weight polyol has a number average molecular weight of from about 250 to about 12,000 and the low molecular weight polyol has a number average molecular weight of from 60 to about 250. 
     
     
       40. The radiation-curable polyurethane of  claim 1  wherein the high molecular weight polyol has a number average molecular weight of from about 400 to about 6,000.